It is known that the storage of data on a recording medium can be accomplished through use of magnetic storage techniques. Magnetic tape is highly desirable because it provides a good medium for storing large amounts of computer data and information. Typically, these magnetic tapes are stored in magnetic tape cartridges. One type of magnetic tape cartridge that is widely used in the industry is referred to as the 3480 cartridge or data card. This type of magnetic tape cartridge is illustrated in FIG. 1.
The cartridge 10 includes a housing 12 having an opening 14 in one comer for permitting the passage of the magnetic tape in and out of the cartridge 10. A centrally positioned opening 16 is provided in the housing 12 to permit access to a unit 18 that is engaged by a computer drive mechanism (not shown) for winding and unwinding the magnetic tape.
As seen in more detail in FIG. 2, the unit 18 includes a spool 20 that is adapted to receive the magnetic tape (not shown). The spool 20 is provided with a hub 22 having teeth 24 on the outer face thereof. These teeth 24 extend around the outer periphery of the hub 22. The hub 22 is also provided with teeth 26 on the inner surface thereof that are adapted to mate with teeth 28 provided on a locking mechanism 30.
The locking mechanism 30 is provided with a hollow stem 32 that is received on an upstanding lug 34 which is fixed to the housing 12. A spring 36 encircles the outer surface of the stem 32 and provides a biasing force that tends to urge the locking mechanism 30 towards the opening 16 in the housing 12. The upstanding lug 34 and the hollow portion of the stem 32 are suitably shaped to ensure that the locking mechanism 30 does not rotate relative to the housing 12.
When the cartridge 10 is not in use (i.e., is not positioned within a computer drive), the spring 36 urges the locking mechanism 30 towards the opening 16 such that the teeth 28 on the locking mechanism 30 engage the teeth 26 provided on the hub 22. In that way, the spool 20 is prevented from rotating. On the other hand, when the cartridge 10 is positioned within the computer drive (not shown) an element on the driving mechanism engages a projection 38 formed on the locking mechanism 30 and pushes the locking mechanism 30 away from the hub 22 of the spool 20. As a result, the teeth 28 on the locking mechanism 30 become disengaged from the teeth 26 on the hub 22 so that the spool 22 is free to rotate.
The driving mechanism (not shown) is provided with teeth that engage the teeth 24 on the hub 22 of the spool 20 in order to drive the spool 20 and thereby result in winding or unwinding of the magnetic tape around the spool 20.
The front face of the spool hub 22 has a ferromagnetic insert 40 secured thereto. The drive mechanism (not shown) is provided with a magnetic portion that attracts the ferromagnetic insert 40, and thus the spool 20, so as to result in engagement of the teeth on the drive mechanism (not shown) with the teeth 24 on the spool hub 22.
As can be seen in FIG. 1, the ferromagnetic insert 40 is provided with a centrally located opening 42 for permitting access to the projection 38. The insert 40 is also provided with several other holes 44 for securing the ferromagnetic insert 40 to the plastic hub 22. The spool hub 22 is typically fabricated of plastic material and can be provided with upstanding plugs that extend through the holes 44 in the ferromagnetic insert 40. Once the ferromagnetic disk 40 is mounted on the spool hub 22 with the plastic plugs extending through the holes 44, the plastic plugs on the hub 22 can be heated and slightly melted in any suitable way, such as by sonic welding, so that the plastic fills the holes 44. In this way, the insert 40 becomes attached to the hub 22.
Referring to FIG. 3, the holes 44 in the insert 40 are typically formed by first punching the insert 40 to result in holes having a diameter that is slightly smaller than the ultimate diameter. Thereafter, a punching operation is performed from both sides of the insert 40 with a slightly larger punch so as to result in holes 44 having the desired diameter. This finishing punch operation results in the formation of annular ridges 46 on the inner surface of the holes 44. These annular ridges help provide a positive attachment of the plastic plugs on the spool hub to the disk 44.
In practice, it is necessary that this finishing punch operation be performed from both sides of the insert 40 to ensure that the resulting insert 40 is symmetrical (i.e., symmetrical about a plane located midway between opposite faces of the insert). In that way, the insert 40 can be mounted on the spool hub with either of the faces of the insert facing the spool hub. If this finishing punch operation were only carried out from one side of the insert, the result would be a non-symmetrical insert (i.e., non-symmetrical about a plane located midway between opposite faces of the insert). Such a non-symmetrical insert could only be mounted on the spool hub in one way and would require painstaking effort to ensure that the insert 40 is positioned on the hub 22 in the appropriate manner. Such painstaking efforts would not be conducive to facilitating attachment of the inserts 40 to the hub 22 in a relatively expedient and possibly automated manner.
Unfortunately, there are several disadvantages associated with the known types of ferromagnetic inserts such as illustrated in FIG. 3. In one respect, since the finishing punch operation is carried out from both sides of the insert 40, the resulting insert typically includes two annular ridges 46 that are spaced apart by a space 48. During use, when the ferromagnetic insert 40 is attracted to the magnetic element on the computer driving mechanism, the insert 40 must be able to withstand a certain pull-out force. In that regard, the spaced-part annular ridges 46 and their interaction with the plastic plugs extending from the hub 22 may not be sufficient to withstand this pull-out force. Indeed, the relatively thin nature of the annular ridges 46 may not be capable of withstanding the repeated force that tends to pull the insert 40 away from the spool hub. Moreover, since the annular ridges 46 only extend a very short distance towards the center of the hole 44, the annular ridges 46 may not provide sufficient interaction with the plastic plugs on the spool hub so as to withstand the repeated force that tends to pull the disk 40 away from the spool hub. Over time, this may result in loosening of the insert 40 relative to the spool hub 22.
Another disadvantage associated with the known type of insert 40 is that it is relatively costly to manufacture. This derives from the fact that the thickness of the insert 40 is 1.55 mm. As the inventor herein has discovered, the function served by the insert 40 does not require that the insert 40 possess such a thickness. Indeed, it has been found that certain advantages can actually be achieved by fabricating the insert to have a much smaller thickness.